Apparatus for determining the transmissivity of an optical medium

Abstract

Three photometers are positioned at three points P 1 , P 2 and P.s3, aligned with each other and with an illuminating flare, and located at equal distances d from each other, with the middle photometer at a distance D, greater than d, from the flare; the illuminations E 1 , E 2 , and E 3 simultaneously received by the three photometers from the flare are recorded; and the transmissivity T, or transmission per mile, of the atmosphere traversed by the light is calculated from the formula: ##EQU1## where the E values are in foot candles and d is in miles.

What is claimed is: 
     
       1. An apparatus for determining the transmissivity T of a gas medium on the basis of the following equation ##EQU13## comprising the combination of a source of radiation in a gas medium, and three radiation sensors S 1 , S 2  and S 3  for measuring the amounts of radiation E 1 , E 2  and E 3  respectively received thereby from said radiation source in a gas medium, wherein (a) said sensors are aligned with each other and said radiation source will equal spacing d between sensors S 1  and S 2  and sensors S 2  and S 3 , the middle sensor S 2  being at an unknown distance D greater than d from said radiation source, and   (b) said sensors are located at distances D-d and D+d respectively from said source, where d is smaller than D.     
     
     
       2. An apparatus according to claim 1, wherein the radiation source is an illuminating flare in the atmosphere and the radiation sensors are photometers.